1. Field of the Invention
The present invention refers to a piston servo-actuation main system, of electromechanical and hydraulic type, specially conceived for its use in global servo-actuation systems exhibiting the following characteristics: a) high reliability, b) minimum effect of the failures of the main system on its operation; c) fast and efficient main system failure detection, confirmation and compensation; d) easy logic in the dedicated control system; e) global servo-actuation system reversibility, i.e., ability to go back to normal operation mode should spurious failures occur, thus preventing loss of redundancy.
This invention refers to a piston servo-actuation main system, of electromechanical and hydraulic type, specially conceived for its use in global servo-actuation systems where are required aspects such as: a) high reliability, b) minimum effect of the failures of the main system on its operation; c) fast and efficient main system failure detection, confirmation and compensation; d) easy logic in the dedicated control system; e) global servo-actuation system reversibility, i.e. ability to go back to normal operation mode should spurious failures occur, thus preventing loss of redundancy.
The piston servo-actuation main system is to be connected to a pump able to provide it with hydraulic fluid pressurised flow. Such pressures and flows should be sufficient to enable system operation at any time.
2. Description of Related Art
Many different types of piston servo-actuation are known, most consisting of single or two stage and three or four way servovalves, depending upon the geometry and requirements of piston operation. Whenever a very high reliability of the global servo-actuation system is required, it is usual to provide it with a back-up servo-actuation system (active or inactive) which provides redundancy of the operation on main system failure events. Those failures are usually detected by the control system through the use of an actual piston position signal measured by means of a position transducer and a particular software logic which allows confirming the failure and then transferring control to the back-up system by electrical actuation of electro-hydromechanical components in the global actuation system.
The aim of the present invention is developing a piston main servo-actuation system which offers, in contrast with the methods mentioned above, a self-contained failure detection logic allowing the introduction of a back-up actuation system without any need for the electronic control system to play any role in the process, thus preventing any problem associated to the typical ways electronic controls systems accomplish the detection, confirmation and compensation of main system failures. In the event of a main system failure the reaction against it would then be self-contained and the only effect on the system would be loss of redundancy of the affected function. This system also allows testability of the electromechanical components it consists of either before or after every operating cycle so as to ensure complete availability of the system to perform next cycle.
The objective claimed above is basically achieved, according to the present invention, by means of a piston servo-actuation system of the type described above consisting, in opposition to the typical systems, of two servovalves of the same design, fed by a high pressure supply line and a low pressure spill line, which position a piston mechanically linked to a position transducer, according to the electrical demand supplied by the position feedback control loops to the torquemotors of the servovalve. These control loops receive the piston position demands and are both fed back with the position signal supplied by the position transducer. Each servovalve is provided with a control line which are connected to opposite sides of the piston, thus forming a hydraulic bridge configuration formed by the control lines regulated by the servovalve restrictions. The system is completed with two similar design pressure select valves featuring spool type, four-way, constant area and balanced against either springs, which receive pressure from opposite sides relative to their springs of a working line, set by the supply line and the spill line pressures by means of a potentiometer. The two pressure select valve will control in parallel as a function of their positions if the supply line, fed to the select valves, will be connected to the outlet line, or state line, which will stay either at low pressure of the spill line via a connection through a restriction or at high pressure of the supply line, which may serve as a criteria to, by means of other methods different to this invention, either transfer piston control to an alternative system, disconnecting the system described, or else transfer control completely, including piston and position transducer, to an alternative system.
Should the servovalves be three-way, either single or two stage, both servovalve control lines, one from each, connected to opposite sides of the piston, will be provided with extensions which will act as reference lines connected to the free side of the select valves opposite to that receiving the working line.
Should the servovalves be four-way, either single or two stage, two separate hydraulic bridge configurations would be obtained; one formed by the two control lines of the servovalves which are connected to opposite sides of the piston, the other formed by the other two control lines of the servovalves, joined each other in a short-circuited hydraulic bridge by means of a line acting as a reference and connected to the two free sides of the select valve opposite to those receiving the working line.
The constitution and features of this invention, such as they are covered in the claims as well as the advantages obtained could better be understood with the following description, made with a reference to the figures attached, in which it is shown in a schematic way and as non limiting instance possible ways of implementation.